Electrical control apparatus



Apri 2 1954 J. J. CZAJA 2,675,230

ELECTRICAL CONTROL APPARATUS Fild Feb. 23, 1951 OOU'OOOtn F ggs/47 INVENTOR. 72% 741 W2 Vfiuq- 7 ram/5V5.

Patented Apr. 20, 1954 UNITED STATE.

ELECTRICAL CONTROL APPARATUS John J. Czaja, Detroit, Mich, assignor to Weltronic Company, Detroit, Mich, a corporation of Michigan Application February 23, 1951, Serial No. 212,469

14 Claims.

This invention relates generally to electrical control apparatus and more specifically to such an apparatus for controlling the flow of electrical current to a machine requiring a flow of coolant.

An object of this invention is to provide a sequencing network for controlling the various operational steps of a current consuming apparatus which will automotically control the flow of coolant to such apparatus.

Another object of this invention is to provide such a network which will maintain the coolant flow for a desired interval subsequent to termination of the operation of the apparatus.

Another object is to provide such a network which during continued operation will maintain a flow of coolant but upon termination of such operation will automatically shut off the flow of coolant.

Other objects of this invention will be apparent from the specification, the appended claims, and the drawing, in which the sole figure thereof diagrammatically shows a welding machine sequencing network embodying the invention.

Other features of the shown sequencing network are described and claimed in copending applications of Cletus J. Collom, Serial No. 212,467, filed February 23, 1951, and Serial No. 216,621, filed March 20, I951, abandoned in favor of continuation application Serial No. 290,550 filed May 28, 1952, and in a copending applica tion of Lauren F. Elliott, Serial No. 214,987, filed March 10, 1951, now Patent No. 2,656,461, dated October 20, 1953.

Generically the invention comprises an electrical network comprising valves IV through lV which control the various operating functions of welding machine as, for example, the squeeze time interval, the Welding time interval, the hold time interval, the off time interval and the in terval during which coolant is supplied to the welding machine. The length of squeeze time is controlled by network I, the length of the weldtime by means of network 2 while the hold time and off time are controlled by the networks i and 55 respectively. The sequencing network is operable to initiate the flow of coolant substantially simultaneously with the initiation of operation of the sequencing network and a timing network 8 acts to control the time during which the coolant is permitted to flow subsequent to the completion of a complete sequencing operation of the network. Preferably the time afforded by the network 8 is greater than that of the network 6 so that, when the sequencing network is operated continually, the flow of coolant will not be interrupted but flow of coolant will be interrupted shortly after the use of the sequencing'network has been discontinued.

For the inter sts of simplicity neither the electrical nor the fluid circuit for the coolant has been shown other than the control relay CBS which controls the stopping and starting of the coolant flow in accordance with the closed or open position of the normally open contacts CRla. Likewise the fluid circuit and the detailed electrical circuit therefor for controlling the position of the welding electrodes is not shown other than as is shown iragmentarily by the normally open contacts CRZa of the control relay CR2. Similarly the specific circuit controlling the flow of current to the welding electrodes and the welding electrodes themselves are not shown other than by the normally open contacts CR3! of the welding current control relay CR3.

The sequencing network receives its energization from a transformer Tl having a primary winding it which is connected through suitable switches, not shown, for energization from the lines Li and L2 which may be connected to any suitable source of alternating current energy. The secondary winding E2 of the transformer has one terminal 53 thereof connected to a bus BI and its other terminal l5 connected to the bus B2 whereby alternating current electrica1 potential is applied between the busses. The valves iV, lV, 5V and 5V each have their cathodes connected by means of conductors M, l6, l8 and 20 respectively to the bus B2 while the anodes of the valves 2V and 3V are connected to the bus B2 by conductors 22 and 24 respectively. The anode of valve W is connected by a conductor 26 and a resistor R! to the bus B2. Interposed in series in the conductor 22 is the energizing winding 28 of a control relay CR4, connected in series in the conductor 2c is an impedance network 39, and connected in series in the conductor 26 is the off time network 6.

The anode of the valve W is connected through the energizing winding 32 of a control relay CR5 and the winding 34 of the control relay CR2 to a third bus B3, the windings 32 and 34 being parallelly connected with each other. If desired a single relay having the proper number of contacts could be substituted for the shown two relays. The bus B3 is selectively connected to the bus Bi and terminal it by means of two parallel circuits, one of these includes the normally open contacts CREia of the relay CR5, the other includes the normally closed contacts CRGa of the relay CR5 and the normally open contacts of the pilot switch SWI.

The cathode of the valve 2V is connected by means of conductor 3% through the normally open contacts CREb or the relay CR5 to the bus Bl. The cathode of the valve 3V is connected by means of conductor 33 and the normally closed contacts CRt c of the relay CR5 to the bus BI and is also connected through resistor R13 to the bus B2. The anode of the valve tV is connected through the energizing winding 46 of the coolant control reiay cm and conductor 42 to the bus B l A pilot light Pill may be connected in parallel with the winding dc to indicate, when illumihated, the fact that the coolant supply is turned on. The anode of the valve iiV is connected through the energizing winding i -i of the Welding current control relay CR3 to a conductor The conductor is connected to the bus through two parallel circuits, one of which in-- clucles the normally open contacts oi the relay CR2 and the other of which includes the energizing winding of the safety control relay CR6 and a rectifier R'Ei. A capacitor is connected in parallel. with the winding al A we1dno-welcl switch SW2 is connected in series with both oi these parallel circuits so that, ii desired, the switch SW2 may be moved to open position and the sequencing network you through a se quencing operation without actually providing for the flow of welding current.

The anode of the valve 6V is connected through the hold time network to a conductor 50 which is connected through a resistor R2 to the bus Bl. The cathode oi the valve 'iV is con nected by a conductor 52 to the bus As shown, the resistor R2 is connected between the conductor and the bus Bi and the resistor El between the bus and the conductor In order to establish a potential of the conductors 58 and with respect to the Bi and 332 respectively, a third resistor l-tt connected in series between the resistors Hi and B2. if desired, a capacitor C3 may be arranged shunt relation with the resistor to phaseshiit the voltage which appears across resistors Bi and R2 so that the control. voltages provided thereby lead the anode voltages of the respective valves.

The controlling grid of the valve 2V is connected through the usual grid current controlling resistor to one terminal of the squeeze time network '5. The other terminal or this network is connected to the bus iii. The control grid of the valve 3V is connected through the usual grid current controlling resistor to one terminal 58 of the network 8, the other terminal fill of which connected to the bus Bl. The controlling grid of the valve is connected through the usual grid current controlling resistor to the common terminal iii between. the network fill and the anode of the valve 3V. The controlling grid of valve 'EV is connected through the usual grid current controlling resistor to the common terminal between the hold time 'networir and the anode of the valve V.

The control bias applied between the grid to cathode of the valves 5V and @V is derived from a chargeable capacitor Ci. which, in the normal position of the relay C is maintained fully charged from a rectifying network 62 which is energized by the potential appearing between the bosses Bi and B2. The negative output bus of the network 52 is connected to the negative terminal 66 of capacitor C t which connected through parallelly connected resistor and capacitor C5 to the conductor iii and cathode of valve 5V.

The positive output bus f the network is connected to one contact "it of a single pole double throw switch actuated by the relay CR4 and having a movable arm iii eng geable with contact Hi When the relay one :s de-energized and engageable with a contact iii when the relay CR4 is energized. The arm '16 is directly connected to the positive terminal 68 of the capacitor C-i. conductor all connected through the usual grid to current controlling resistor to the grid of the valve 5V is connected to the contact it and to one terminal 82 of the weld time network 2. The other terminal fi l of the network 2 is connected to the bus 64 and thereby to the negative terminal 66 of the capacitor Cd. The network 2 comprises one or more series connected resistors R6, R-i and RB having parallelly connected therewith the resistor R9. One or more of the resistors R6, and R8 may be adjustable for determining the length of time required to discharge the capacitor C4.

Normally :a unidirectional substantially constant potential is maintained across the resistor and capacitor R5, C5 by the transformer having its primary winding connected between the bosses Bi andIBtl. The polarity or the potential so applied by'the transformer T3 is in a direction to maintain a negative grid-to-cathcde Or blocking bias voltage on the'valve 5V.

The positive terminal $3 of the capacitor C4 is continually conn cted by means or condo and the usual grid current controlling r" istor to the grid oi": the valve 6V. .In this in be noted that the cathode of the valves or and 6V are of the same potential each being directly connected to the bus B2.

it is believed that the remaining details of construotionimay 'bestbe'understood from a description of operation of the network which is as fol lows:

Upon energization of the winding ill of the transformer Tl, the winding l2 will establish an alternating potential between the busses Bi and B2. The valve 3V will immediately commence to conduct establishing a circuit from tie bus B2 through the network 30, the valve 3V, the normally closed contacts CREic, and the conductor 38 to the bus Bl. This will establish a voltage diiierential JQICIOSS the network 35 which is applied between the grid and cathode of the valve -lV maintaining it blocked and the relay CR: oleenergized. The network B'Zwill also be energized to establish a positive to negative voltage between the busses l2 and 84 which due to the now dc-energized condition of the relay will be applied. to charge the capacitor C4.

The valve 5V will be held in a nonconductive condition by the voltage established across the resistor and capacitor R5, C5 by the transformer T3 which was energized concurrently with energization of the bosses BI and B2 that even though the weld-no-weld switch SW2 is in its normally closed position .asshown, the relays and CR8 will remain ole-energized. The charged condition of the capacitor Ct will overcome the blocking bias voltage afforded by the transformer T3 between the grid :and cathode of the valve EV which valve will then be in a conductive condition and current will flow from the bus through the resistor R2, the conductor 50, the hold time network 4, the valve Wand conductor to the bus Such flow of current through the valve 3V establishes a potential across the network. c which is applied as a blocking potential between the grid and cathode 'of the valve TV which will hold this valve blocked whenits anode-cathode circuit is completed. At the same time current for charging the network i will now from the bus .51 through the resistor R2, conductor 5B, the network 1, grid to cathode conduction in. the valve 2V and through the resistor Rib to the bus B2. This flow of current will place a charge across the capacitor Cl 2 of the network I.

When it is desired to initiate the operation of the welding apparatus, the switch SW! is momentarily closed connecting the bus B3 to the bus Bi completing the anode-cathode circuits for the valves IV and 1V. Since the valve 1V is biased into a nonconductive condition above set forth, it will not conduct and there will be no potential established across the network 6 to bias the valve IV into a nonconductive condition. Therefore upon closure of the switch SW I, as soon as the bus B3 becomes positive with respect to the bus B2, current will flow therefrom through the windings 32 and 34, the valve iV, and conductor It to the bus B2. This energizes the relays CR2 and CR5 closing the contacts CRZa, C3212, 035a, and CR5!) and. opening the contacts CBS J.

Closure of the contacts 0135a establishes a ho1ding circuit by-passing the manually operable initiating switch SW! so that it may be subsequently released without interfering with the sequence of operation which has then been initiated. 010* sure of the contacts CRSZ) transfers the potential of the cathode of the valve 2V from substantially that of the bus B2 to that of the bus Bl thereby terminating any further flow of charging current to the capacitor CIZ of the network I. The network I which has been maintaining the valve 2V in a nonconductive condition begins to discharge through the discharge resistors Elliot and R121). Opening of the contacts CR50 opens the anodecathode circuit of the valve 3V terminating further energization of the network 36 and trans ferring the potential of the cathode of the valve 3V from that of the bus Bi to substantially that of the bus B2. Transferring of the potential of the cathode of the valve 3V permits a charging lrrent to flow from the bus Bl through the network 8, grid to cathode conduction in the valve 3V, and resistor Hi3 to the bus B2. Closure of the contacts CRZa completes a circuit for the usual ram mechanism, not shown, whereby the electrodes, not shown, are moved against the workpiece, not shown. Closure of the contacts C3229 is without immediate efiect since at this time the valve EV is nonconductive as above described.

De-energication of the network 3K3, which occur rapidly, removes the blocking bias voltage between the grid and cathode of the valve iV which then begins to conduct causing current to flow from the bus Bl through conductor 42, winding 42! of relay CRI, valve 5V and conductor is to the bus B2. Energization or the relay CR! closes the contacts CPtia thereof to start the flow of coolant to the welding machine, not shown.

At the end of a predetermined time interval subsequent to closure of the switch SW5, the capacitor CiZ will have discharged sufliciently through the resistors RIZa, and R121: to remove the blocking bias potential between the grid and cathode of the valve 2V which then conducts cstablishing a circuit between the bus B2 through conductor 22, winding 28 of the relay ORA, valve 2V, conductor 36, and the now closed contacts (DE-15b to the bus Bl. Energization oi the relay CR5 moves its switch arm 16 out of engagement with the contact 14 and into engagement with the contact '58 whereby the capacitor C4 is disconnccted from the charging network 52 and connected to its discharging network 2.

Connection of the capacitor 04 with its discharge network 2 places the potential existing across the capacitor C4 and the resistor R9 in opposition to the blocking potential appearing across the resistor and capacitor B5, C5 raising the potential of the grid of valve 5V relative to the cathode potential of the valve 5V sufiiciently to permit the valve 5V to conduct. Conduction oi the valve 5V closes a circuit from the busBl through the now closed contacts CR2b, conductor l6, winding 4d of the relay CR3, valve 5V and con ductor [8 to the bus B2. Upon energization, the relay CR3 closes its contacts CRSa to cause cur-- rent to flow between the electrodes which have now been clamped against the work. Any suitable control circuit actuated upon closure of the contacts CRZia may be used to control the flow of welding current between the welding electrodes and therefore the details of this circuit have been omitted in the interests of simplicity.

The capacitor Cd is now discharging through the resistors Rd to R9 and after a predetermined time interval which is the welding time interval, the charge across the capacitor C4 will decrease sufiiciently so that the blocking potential provided by the resistor and capacitor B5, C5 will overcome the unblocking potential of the capaci tor Ct whereby the valves 5V and il will be rendered nonconductive. Rendering of the valve 5V nonconductive de-energizes the relay CR3 permitting its contacts C330: to open and to termihate the flow of welding current between the welding electrodes. Rendering of the valve 53V nonconductive terminates further charging of the capacitor Chi oi the network l which then begins to discharge through the resistors Rita and Ri tb for measuring out the hold time or time period in which the electrodes are held against the workpiece subsequent to termination of the flow of welding current and prior to the withdrawal of the electrodes from the workpiece.

At the end of this predetermined time period, the charge across the capacitor CH5 will have decreased sufiiciently so that the unblocking potential supplied by the resistor R2 will overcome the blocking potential supplied by the network a and the valve EV will then commence to conduct. Conduction of the valve 5V establishes a circuit from the bus B2 through the resistor Hi, the network 6, valve l'V, conductor 52, bus 33, closed contacts CR5a to the bus Bl. This estab" lishes a voltage drop across the network 6 which is applied between the grid and cathode of the valve iV rendering this valve nonccnductive.

Rendering of the valve IV nonconductive dcenergizes the windings 32 and 36 whereby the relays CR5 and CR2 open their normally open contacts CRfia, Cl'tiib, C324; and CR2?) and close the normally closed contacts CRfic. Opening of the contacts CHM d e-energizes the circuit controlling the clamping of the electrodes perrnitting the rain mechanism, not shown, to move the electrodes away from the work. Opening of the contacts CR2!) is without immediate effect due to the now nonconductive condition of the valve 5V. Opening of the contacts CRdo: opens the by-pass holding circuit around the switch SW! and the contacts CRta. Assuming that the switch SW! has been maintained closed, the opening of the contacts CREa will be without effect. If, however, the switch SW! has been opened, opening of the contacts Gil-ta de energizes the bus Opening of the contacts CR5!) transfers the potential or" the cathode of the valve 2V from that of the bus B5 to substantially that of the bus B2 permitting a recharging of the capacitor C52 of the network Closure of the contacts CREc transfers the potential of the cathode of the valve 3V from substantially that of the bus B2 to that of the bus Bl terminating further, flow of charging current to the capacitor C i E ofjthe network a thereby causing the capacitor Cid to discharge through the resistors Rita and Rlb. After a predetermined time interval the charge across the network 3 will be reduced sufficiently so that the valve 3V will again conduct establishing a potential across the network 3t which is applied a blocking potential between the grid cathode of the valve 4V blocking this valve permitting the contacts CRla of the relay CR5 to open and terminate further flow of coolant to the welding apparatus.

If it is assumed that the switch SW was opened prior to timing out of the off time net work 6, opening of the contacts GEM opens the anode circuit for the valve 7V terminating fur-- ther energization of the network a whereby its now charged capacitor C16 commences to dis charge through the resistors Rita and Rltlb. At the end of a predetermined period known as the off time, the blocking bias potential between the grid and cathode of the valve 5 V will be removed. However, since switch SW! was opened prior to the timing out of the network this without effect. If, however, the switch SW! is still maintained closed, timing out of the network 5 will initiate a new sequencing cycle, as above described. Normally the network it will not be adjusted to time out prior to the timing out of the network 6 and the initiation of a new cycle of operation will occur prior to the reconduction of the valve 3V and blocking of the valve 4V to tie-energize the coolant control relay #SRI to terminate further coolant flow.

As just described, the sequencing network will continue to sequence the welding apparatus just as long as the switch SWl is maintained closed. If it is desired to sequence the welding apparatus through only one welding cycle irrespective of how long the switch SW l is maintained closed, the single-repeat switch SW3 is moved from the shown B position to the S position. Such a positioning of switch SW3 will not interfere with the normal timing aifordecl by the condensers Cd and CM to measure out the weld time and hold time intervals nor the timing function of the network 8 for controlling the how of coolant. Such positioning of the switch SW3 permits energize.- tion of the relay CR4 and consequent closure of its contacts CR la to establish a holding circuit around the contacts CR5Z7 to connect the cathode of the valve 2V through conductor 86, the closed contacts CR la, the single-repeat switch SW3 and conductor 38 to the bus 133 so that the valve 2V will remain conductive as long as the switch SW5 or contacts CRM are closed. With such a hololing circuit, the establishment of a potential across the off time network 6 and consequent blocking of the valve IV will not cause an interruption in the circuit for the winding 23 of the relay CR4. As long as the relay CR4 is maintained energized, condenser C4 cannot be re charged and after the condenser C l discharges, as above described. in connection with repeat operation to cause the valves 5V and 6V to blocl: the valves 5V and 6V will remain nonconductiv... its long as valve 5V is nonconductive, valve TV will conduct to maintain the network c energizcd and the valve lV blocked.

In order to reset the sequencing network for a subsequent operation, it is necessary to l'i'lO- mentarily open the switch SW5 which terminates further conduction of the valve iv and permits the relay to open its contacts Cit ic since the circuit therethrough is broken by the open ing of switch SWl. With the single-repeat switch in its single operative position, it shorts out the resistor RlGa permitting the capacitor Clii to discharge very rapidly through the re sistor arse afiording subsequently no or" time interval. .An almost immediate reclosure of the switch SW1 will therefore start a new sequencing operation.

Let us first assume that for some reason or other the valve 5V loses control and becomes conductive during an interval in which the switch SW1! is open and the network is not performing a sequencing operation. Under such conditions, the relay CR2 will be ole-energized so that its contacts CR2?) will be open. The cur-- rent flow between the bosses Bi and Bi. therefore will flow through the windings 43 it in series. The winding 43 has such a high impedance that with the voltage applied between the Bi and E2, the winding as is held below a minimum predetermined value at which the relay CR3 will not act to close its contacts CRta. Therefore the electrodes cannot be energized, Energization of the winding 48 in this manner will actuate the relay CR6 open the contacts CRta thereof. Opening of the contacts 036a renders the closure of switch SW1 ineffective to connect the bus B3 with the bus since the switch SW! and the contacts CRtc in series with each other between the bosses Bi and 133. Therefore the welding apparatus cannot be sequenced with a defective valve 5V or some other type of short circuit whereby the windings 48 and M are serially energized between the bosses Bi and B2.

Let us now suppose that the valve 5V becomes shorted or otherwise goes out of control and into a conducting condition during the time interval subsequent to energization of the relays CR2 and Under such operation conditions, the relay CR6 will not be energized since its winding d8 is shunted by means of the now closed contacts CR2b. However as soon as the sequence network has completed a sequencing operation and the off time network 8 has become energized to hlocl; the valve W, the relays CR2 and CR5 will move to a tie-energized position opening the contacts CR2!) connected in shunt with the winding 48 and inserting the Winding 48 of the relay CR6 in series circuit with the winding M. This reduces the degree of energization of the relay CR3 so that the contacts CRBa move to open position terminating further flow of electrical energy to the electrodes. Energization of the relay CR5 also caused the contacts CR Sa to open so that the switch SW1 is ineffective to conneot the busses Bi and B3. In a normal system and considering the worst condition in which the valve 5V failed just at the instance the valve EV commenced to conduct, it will amount to only a relative short time during which current will fiow through the electrodes and will not permit too serious damage to the welding apparatus.

What is claimed and is desired to be secured by United States Letters Patent is follows:

i. In a sequencing network for operated apparatus, a plurality of sequentially operated circuits for controlling the operations of said apparatus, means for initiating sequential operation of said circuits, an electric valve having a pair of principal electrodes control elec trode, a first means including an impedance element connecting one of said principal electrodes to one side of an alternating current supply, a second means connecting the other of said prlncipal electrodes to the other side of such supply, switch means in said second connecting means normally maintained in a circuit making position, means responsive to the operation of one of said sequentially operated circuits for actuating said switch means to a circuit opening position, an impedance network connected between said control electrode and such supply other side, means responsive to the conductivity of said valve for controlling an operating characteristic of such apparatus, and means responsive to the operation of another of said circuits for restoring said switch means to said circuit making position.

2. In a sequencing network for an operated apparatus, a plurality of sequentially operated circuits for controlling the operations of said apparatus, means for initiating a sequential op eration of said circuits, an electric valve having a pair of principal electrodes and a control electrode, a first means including an impedance element connecting one of said principal electrodes to one side of an alternating current supply, a second means connecting the other of said principal electrodes to the other side of such supply, switch means in said second connecting means normally maintained in a circuit making position, means responsive to the operation of one of said sequentially operated circuits for actuating said switch means to a circuit opening position, an impedance network connected between said control electrode and the other side of such supply, a second electric valve having a pair of main electrodes and a control electrode, means including a controlling device connecting said principal electrodes between the sides of such supply, means deriving a potential from that appeering across said impedance element and connected between said control electrode and one of said main electrodes of said second valve, and means responsive to the operation of another of said circuits for restoring said switch means to said circuit making position.

3. in a sequencing network for an operated apparatus, a first and second bus adapted to be energized from an alternating voltage supply, a third bus normally disconnected from said second bus, a plurality of sequentially operated circuits for controlling the operations of said apparatus and. energized from said busses, means for connecting said second and third busses for initiating a sequential operation of said circuits, an electric valve having a pair of principal electrodes and a control electrode, a first means including an impedance element connecting one of said principal electrodes to said first bus, a second means connecting the other of said principal electrodes to said second bus, switch means in said second connecting means normally maintained in a circuit making position, means responsive to the operation of the first to be operated of said sequential circuits for actuating said switch means to a circuit opening position, an impedance network connected between said control electrode and said second bus, means responsive to the conductivity of said valve for controlling an operating characteristic of such apparatus, and means responsive to the operation of the last to be operated of said circuits for restoring said switch means to said circuit making position.

4. For use with a welding machine having electrodes movable toward and away from a workpiece and having an electrical circuit including the electrodes and having a coolant fluid flow circuit, the combination of a first means for corn trolling the movement oisuch electrodes against such workpiece, second means for controlling the flow of current in such electrical circuit, third means for controlling the movement of such electrodes away from such workpiece, fourth means interconnecting said above-mentioned means for sequential actuation, fifth means for controlling the flow of coolant, sixth means normally maintaining said coolant controlling means in a condition to prevent flow of coolant in such coolant circuit, initiating means for actuating said first controlling means, said initiating means also being operatively connected with and for rendering said sixth means ineiiective to prevent flow of coolant, time delay means controlling the restoring of said sixth means to its normal flow preventing condition, and means responsive to third means for actuating said time delay means whereby such coolant flow is prevented subsequent to the timing out of said delay means.

5. For use with a welding machine having electrodes movable toward and away from a workpiece and having an electrical circuit including the electrodes and having a coolant fluid flow circuit, the combination of means for controlling the movement of such electrodes against such workpiece, means for controlling the flow of cur-- rent in such electrical circuit, means for controlling the movement of such electrodes away from such workpiece, means interconnecting said above-mentioned means for sequential actuation, means for controlling the flow of coolant includ ing means normally maintaining said coolant controlling means in a condition to prevent flow of coolant in such coolant circuit, initiating means for actuating one of said controlling means, said initiating means also being operatively connected with said coolant flow controlling means and operable to cause the latter to initiate a flow of coolant, time delay means controlling the restoring of said coolant flow controlling means into normal flow preventing condition, and means responsive to another of said controlling means for actuating said time delay means whereby such coolant flow is prevented subsequent to the timing out of said delay means.

6. In a control circuit for a welding machine requiring a flow of coolant during its operation, a sequencing network for controlling the sequence of operation of such machine, a coolant flow control means, means for initiating an operation of said network, means actuated as a consequence of an operation of said initiating means for actuating said coolant control means to a condition to permit flow of coolant to such machine, and time delay means actuated as a consequence of the actuation oi? the final sequencing step of said network for holding said coolant control means in its flow permitting condition for a desired time interval subsequent to completion of the sequencing operation of said network.

7. In a control circuit for a welding machine requiring a fiow of coolant during its operation, a sequencing network for controlling the se uence of operation of such machine and including the step of moving welding electrodes out or" engagement with a workpiece, a coolant flow control means, means for initiating an operation of said network, means actuated as a consequence of an operation of said initiating means for actuating said coolant control means to a condition to permit flow of coolant to such machine, and time delay means controlling the actuation of said coolant control means to a condition to prevent flow of coolant, said delay means being actuated as a consequence of the operation of said network to control the said step of moving said electrodes out of engagement with a workpiece.

8. In a control circuit for welding machine requiring a flow of coolant during its operation, a sequencing network controlling the movement of welding electrodes toward and away from the workpiece, means operable to initiate a flow or coolant to such machine, said means being actuated as a consequence of the rendering of said network in a condition in which it is effective to move such electrodes toward such workpiece, and means operable to terminate such coolant flow, said last named means being actuated as a consequence of the rendering of said network in a condition in which it is effective to move such electrodes away from such workpiece.

9. In a control circuit for welding machine requiring a flow of coolant during its operation, a sequencing network controlling the movement of welding electrodes toward and away from. the workipece, means operable to initiate a flow of coolant to such machine, said means being actuated as a consequence of the rendering of said network in a condition in which it is effective to move such electrodes toward such workpiece, means operable to terminate such coolant now, said last named means being actuated as a corn sequence of the rendering of said network in a condition in which it is effective to move such electrodes away from such workpiece, and time delay means for providing a time delay between the actuation of said second named mean and. the actual stopping of such flow.

10. In a control circuit for an apparatus re quiring a flow of coolant during its operation, a sequencing apparatus including a plurality of sequentially operated circuits for controlling the operation of said apparatus, an electric valve having a pair of principal electrodes and a con-- trol electrode, an energizable element, main cuit means connecting said element to principal electrodes, a coolant flow controlling connected to be actuated by said element, a cur rent controlling device controlling said circuit means and having a first current controlling condition in which the energization of said element is under control of said valve, said current controlling device having a second current con trolling condition in which said element is maintained in a first condition irrespective of the conductive condition of said valve, a timing means set as a consequence of the actuation of said current controlling device to its said second condition, a bias circuit controlled by timing means and connected between said control trode and one of said main electrodes, and mea responsive to one of said sequentially operated circuits for actuating said current controlling device to its said second condition to set timing means and to place said element in its said first condition, said last named means being responsive to another of said sequentially operated circuits which is actuated subsequently to said one sequentially actuated circuit for restoring said current controlling device to said first cor dition to initiate a timing function of said timing means and to render the energization of said element responsive to said valve.

11. In a control circuit for a welding machine requiring a flow of coolant during its operation, a sequencing apparatus including a timing device for controlling the flow of welding current such machine, a coolant flow controlling device normally maintained in a condition to prevent the flow of coolant, controlling means actuated as a consequence of the actuation of said apparatus for operating said flow controlling device to permit how of coolant, and timing means including said timing device for restoring said flow controlling device to its flow preventing condition subsequent to the termination of the flow of welding current.

12. The combination of claim 11 in which said timing means includes a second timing device actuated to time out its time interval subsequent to the timing out of said first named timing device.

13. The combination of claim 12 in which means is provided to cause repeat operations of said sequencing apparatus, said sequencing apparatus includes a third timing device to time an interval between the initiation or the timing out of said second timing device and the commencing of a subsequent repeat operation of said sequenc ing apparatus, the timing interval of said third timing device being less than the timing interval of said second timing device so that during repeating operations of the welding machine said second timing device will not time out prior to the starting of such subsequent repeating operation.

14:. For use with a welding machine having an electrical circuit including electrodes movable toward and away from a workpiece and having a coolant fluid flow path, the combination of a plurespectiveiy the movement of such electrodes and the flow of electrical ener y through such electrical circuit, time delay means for controlling the time interval between successive epeating operations of said sequentially operated networks, starting means for initiating plurality of said repeating operations of said sequentially operated networks, coolant flow apparatus for controlling the flow of coolant through such coolant path, said timing apparatus normally being maintained in a condition to prevent such coolant flow, a first controlling means responsive to the actuation of said starting means for actuating said coolant flow appa ratus to permit coolant to how, a second controlling rneans actuated by one of sequentially actuated networks for restoring said coolant flow apparatus to its said normal condition in which flow of coolant is prevented, said second controlling means including a time delaying apparatus to provide time delay interval between the time of actuation of second controlling means by said one sequentially actuated network and the time at which said second controlling means acts to restore said coolant flow apparatus to its normal condition, time delay interval of said delaying apparatus of sa second controlling means being or? greater duration than the total of he time interval provided by said first named time delay means plus any time intervals which may occur in said sequentially operated networks which may be actuated subsequent to the actuation of said second controlling means by said one sequentially actuated network.

References Cited in the file of this patent UNITED STATES PATENTS ll umber Name Date 2,315,916 Whiteley et al Apr. 6, 1943 2,390,981 Bivens Dec. 18, 1945 2,502,876 Mullen Apr. 4, 1950 2,518,118 Bivens Aug. 8, 1950 2,540,514 Elliott Feb. 6, 1951 

